the one thing they do have which puts them at a big advantage is a youth system that consistently produces one, two or three good players every year which make it into the first team squad. i'm sure that this season young players like wellbeck, macheda, diouf (no, not that one), smalling and cleverly will feature and the da silvas will improve. they also have young telented signings like hernandez and obertan.
it will take some doing to replace a whole generation like the one that featured beckham, scholes, neville, giggs etc etc, but i think they have the set up to produce enough talent to keep the first team strong.